Fluorescent lamp with a reflective coating containing tio2 and sb or its oxide



Aprll 23, 1968 R. A. MENELLY 3,379,917

FLUORESCENT LAMP WITH A REFLECTIVE COATING CONTAINING T102, AND Sb OR ITS OXIDE Filed 001?. 27, 1965 RICHARD A. MENELLY INVENTOR.

INVENTOR United States Patent 3,379,917 FLUORESCENT LAMP WlTH A REFLECTIVE COATING CONTAINING TiO AND Sb OR ITS OXIDE Richard A. Menelly, Danvers, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Oct. 27, 1965, Ser. No. 505,354 3 Claims. (Cl. 313-109) ABSTRACT OF THE DISCLOSURE A fluorescent lamp having on the inside surface of its envelope a reflective coating of titanium dioxide containing a small amount of antimony or its oxide, the amount being less than one percent.

This invention relates to fluorescent lamps and particularly to those having a reflector inside the lamp envelope. Such reflectors are used to concentrate the light output for more eflicient use in many fields.

Such lamps are generally of two types. In one type, often called merely a reflector fluorescent lamp, there is a coating of reflecting material, such as magnesium oxide or titanium oxide, around part of the inner surface of the enclosing envelopes, and a coating of phosphor material over the reflector coating and also over the otherwise clear portion of the envelope. In another type of reflector lamp, generally called an aperture lamp, the fluorescent coating extends only part way around the circumference of the envelope, leaving a clear strip or aperture which will generally extend longitudinally if the envelope is tubular. A reflector coating is used between the fluorescent coating and the inside surface of the glass tube. The light is mostly emitted through the clear aperture, which is generally coated with a transparent protective material to prevent discoloration.

The reflector fluorescent lamp has been used for general illumination and also for special illumination of runways, roads, signs and the like. Among other uses, the aperture lamps have been used for various lighting purposes including photocopy work, where a bright linear source is desirable.

It has been well known that the light output of the usual fluorescent lamp suffers a drop-01f during opera tion. Various causes contribute to this, such as deposits of impurities from the cathode materials and formation of oxides of mercury, which deposit on the coating or bulb, and changes in the phosphor itself as regards transformation of ultraviolet radiation to visible radiation. In reflector lamps there was an additional loss in reflectivity of the reflector coating with continued operation of the lamp.

I discovered that when using titanium dioxide as the reflector coating, the gradual decrease in light output due to the loss in reflectivity could be diminished by the addition of antimony trioxide to the titanium dioxide suspension prior to coating the bulb. This increases the lumen maintenance during the life of the lamp, and in addition increases the initial lumen output.

I have discovered that titanium dioxide, when used as a reflector material and exposed to ultraviolet radiation, undergoes a photochemical change, and may be reduced to other oxides or even to the base metal, The oxygen made available within the lamp may combine with the mercury present to form oxides. The products of reduction of the titanium dioxide and the oxidation products formed in the lamps are light-absorbing and when deposited on the reflector surface result in a reduction of reflectivity of the reflector coating.

It appears that the addition of the antimony trioxide, in

ice

certain quantities, inhibits the photochemical activity of the titanium dioxide and the light output and maintenance of the reflector lamp is im roved. The antimony trioxide may undergo some changes under ultraviolet radiation, but the products formed may be white or colorless so that the reflectivity of the material is not substantially changed.

It has been found that the addition of 0.4% antimony trioxide by weight of titanium dioxide has been especially effective in improving light output and maintenance in reflector or aperture type fluorescent lamps. Additions from about 0.1% to about 1.0% by weight have shown beneficial results. The addition of antimony, as a metal, in the same percentage by weight is also effective in improving lamp performance. Even when the lamp envelope is made of a glass containing antimony, the addition of antimony to the titanium oxide in an amount in the above range is needed to attain the results set forth.

This invention may be applied with benefit in other lamp types where titanium dioxide may be used as a reflector material and may be subject to ultraviolet radiation.

The addition of antimony trioxide to the titanium dioxide reflector coating suspension thus results in increased light output and an improvement in maintenance of light output during operation.

The following table illustrates the improvement obtained upon adding 0.4% by weight of Sb O to the titanium dioxide (TiO in the reflector coating suspension.

PERCENT LUhiEN MAINTENANCE FRONT 0 HOURS The addition of Sb O furthermore, does not diminish the initial light output, but tends to increase it. The titanium dioxide used was Titanox grade A-MO of Titanium Pigment Corporation, New York, NY. The Sb O is OP. grade.

Other objects, features and advantages of this invention will be apparent from the following description taken in connection with the attached drawing, in which:

FIGURE 1 shows one form of reflector lamp according to the invention, and

FIGURE 2 shows the aperture form of reflector lamp according to the invention.

In FIGURE 1, the sealed glass envelope 1 which is shown tubular, has the usual electrode 2 at each end, the electrode being supported on two lead-in wires 3, 4 which extend through a glass press 5 in the usual stem 6 at the end of the bulb. The lead-in wires 3, 4 extend into and are attached to the contact pins 7, 8 of a base 9, affixed to an end of the lamp, the contact pins 7, 8 being attached to the base in the usual insulating manner, The sealed tube 1 is filled with an inert gas such as argon at low pressure, for example 2 millimeters, and a small amount of mercury, generally enough to provide a low vapor pressure of between 3 and 15 microns during operation. The reflector coating 10 extends part way around the inside surface of the tube 1 to which it adheres. The fluorescent coating 11 extends over the reflecting coating and also over the remaining portion of the inside surface of the tube 1.

FIG. 2 is the same as FIG. 1 except that the fluorescent coating does not extend all the way around the circumference of the inside surface of the tube 1 but extends only part way around leaving the longitudinal aperture 12. A protective transparent coating, such as shown for example in U. S. Patent 3,141,990, which has the same assignee as the present application, covers the aperture 12 to prevent discoloration.

In the preparation of the lamp the reflector portion of the lamp is first coated with a suspension of TiO parti- 3 cles, the suspension containing Sb O in an amount equivalent to 0.4% by Weight of the TiO and a vehicle composed of a suitable binder and solvent When the binder is ethylcellulose, a suitable solvent is xylol. Other binders can be used.

Subsequently, the clear area of aperture 12 is coated with a transparent layer of a refractory oxide such as described in Patent 3,141,990 assigned to Sylvania Electric Products Inc.

Finally, a suspension of fluorescent phosphor in one or more of the usual binders and solvent is applied over the bulb portion previously covered by the reflector coating.

The tube is then dried and baked in the usual manner to remove the organic materials introduced in the coating process and subjected to the sealing-in, exhaust and finishing processes as carried out in Well known steps in the manufacture of fluorescent lamps.

Although a specific embodiment has been described, various modifications Will be apparent to a person skilled in the art Without departing from the spirit and scope of the invention which is defined in the claims.

What I claim is:

1. A fluorescent lamp having an enclosing envelope, a reflecting coating of titanium dioxide on part of the interior surface of said envelope, said reflecting coating containing an amount of antimony trioxide sufiicient to increase the light output from the lamp but not greater than 1% by Weight of the titanium dioxide and a fluorescent coating over at least part of said reflector coating.

2. A fluorescent lamp having an enclosing envelope, a reflecting coating of titanium dioxide on part of the interior surface of said envelope, said reflecting coating containing about 0.4% by weight of antimony trioxide, and a coating of fluorescent phosphor over said reflecting coating.

3. A fluorescent lamp having an enclosing envelope, a reflecting coating of titanium dioxide on part of the interior surface of said envelope, said reflecting coating containing an amount of antimony metal suflicient to increase the light output from the lamp but not greater than 1% by Weight of the titanium dioxide and a fluorescent coating over at least part of said reflector coating.

References Cited UNITED STATES PATENTS 2,607,014 8/1952 Roy et a1. 313-109 2,637,830 5/1953 Sharkey 313-221 X 3,094,641 6/1963 Gungle et a1. 313 3,115,309 12/1963 Spencer et a1 313-109 X JAMES W. LAWRENCE, Primary Examiner.

DAVID J. GALVIN, Examiner:

P. C. DEMEO, Assistant Examiner. 

